Argus

hundred-eyed giant of Greek mythology, late 14c., from Latin, from Greek Argos, literally "the bright one," from argos "shining, bright" (see argent). His epithet was Panoptes "all-eyes." After his death, Hera transferred his eyes to the peacock's tail. Used in figurative sense of "very vigilant person."

Argus definition

A creature in classical mythology who had a hundred eyes. Hera set him to watch over Io, a girl who had been seduced by Zeus and then turned into a cow; with Argus on guard, Zeus could not come to rescue Io, for only some of Argus' eyes would be closed in sleep at any one time. Hermes, working on Zeus' behalf, played music that put all the eyes to sleep and then killed Argus. Hera put his eyes in the tail of the peacock.